Simulation and Performance Analysis of DWDM System for Long-Haul Transmission using OptiSystem

Design and Simulation of WDM System for Long-Haul Transmission using OptiSystem Md Muzahidul Islam

ForewordWith the development of telecommunication, the requirements of the transmission capacity and service categories are becoming bigger and bigger, under this background, WDM technology emerged. What is WDM?

Objectives

Understand and master the basic concepts and transmission modes, structure of WDM;Understand WDM transmission media;Understand technical principle and key technologies of WDM;Understand technology specification for WDM system.Simulation WDM system.

What's WDM.

Free WayGas StationPatrol Car

What's WDMA short definition of a WDM system, which both applies to Dense Wavelength-Division Multiplexing (DWDM), and Coarse Wavelength-Division Multiplexing (CWDM) is this:In fiber-optic communications, wavelength-division multiplexing (WDM) is a technology which multiplexes multiple optical carrier signals on a single optical fiber by using different wavelengths (Lambdas) of laser light to carry different signals.

Increasing transmission capacity in optical fiber communication systems:laying new fibersCostlyIncreasing the effective bandwidth of existing fibersIncreasing the bit rateIncreasing the number of wavelengths on a fiber

Time Division Multiplexing(TDM)

SDH is the standardized TDM based hierarchical model where the following transmission rates are defined:STM-1: 155 Mbps STM-4: 622 MbpsSTM-16: 2.5 GbpsSTM-64: 10 GbpsSTM-256: 40 GbpsGigabit Ethernet: 1 Gbps, 10 Gbps

Problems for high bit ratescomplex and costlychromatic dispersionnonlinear effectsPolarization Mode Dispersion

SoCombining many wavelength onto a single fiber usingWavelength Division Multiplexing(WDM)

WDM Concept Different signals with specific wavelength are multiplexed into a fiber for transmission.

SDH signal

IP package

ATM cells

Transmission modes Unidirectional transmissionSingle fiber unidirectional transmission

MUXDMUX

OTU

OTUSTATION ASTATION B

Transmission modes - Bi-directional transmissionSingle fiber bi-directional transmission

STATION ASTATION BMUX/DMUXDMUX/MUX

OTU

OTU

Wavelength Division MultiplexingTwo developments have allowed us to start to access the massive bandwidth potential of optical fiber:Optical amplifiers: Provide amplification in the low loss window of optical fiber, and over a broad range of wavelengths (typically 40 nm centred on 1550 nm).Provide transparent operation, i.e. photons in, photons out.Wavelength division multiplexing:WDM components allow us to multiplex together different wavelength channels.

How much bandwidth is there?Assume that our system will operate around 1550 nm and use optical amplifiers. The BW is given by the spectral range over which we get adequate amplification, say 10 dB for 50 km spacing (50 km 0.2 dB/km).

How much bandwidth is there?From earlier diagram, the following spectral bandwidth falls well within the 10 dB gain requirement:

1550 nm1570 nm1530 nm1 = c/f102 = c/f2 = 2 - 1 f = f1 - f2 1 = 1530 nm, 2 = 1570 nm, i.e. 1 2 0

How much bandwidth is there?

In this case, = 40 nm, 0 = 1550 nm which gives:

f = 5 THz (= 5000 GHz)No laser exists that is capable of being modulated over this range.

WDMThese limitations can be overcome with wavelength division multiplexing (WDM).Many different wavelengths (from different lasers) share the same optical fiber.In early WDM, wavelengths were separated by 10 nm; current separation is down to 0.8 nm, and is called dense WDM (i.e. DWDM).

WDMSpectral windows in single-mode fiber offer phenomenal bandwidths:

WDMPresent-day optical devices have bandwidths well below this (< 100 GHz), so to take advantage of the available fiber bandwidth, we can use many wavelengths in the 1.55 m window (where we have the advantage of optical amplification):

Loss,dB/km

1.3m1.55m0.10.2

12n

WDMITU (International Telecommunication Union) have set a standard spacing of 100 GHz for WDM systems (originates from FDM technology). For the 1550 nm window, this is 0.8 nm spacing.

Therefore in our example of 5 THz bandwidth, we have 50 wavelength channels available. If each channel supports 10 Gb/s bit rate for example, then the aggregate bit rate would be 500 Gb/s or 0.5 Tb/s.

Its estimated that with 1 Tb/s we could transmit all the worlds TV station output simultaneously.

Advantages of WDMCapacity upgrades. If each wavelength can support a bit rate of a few Gb/s (40 Gb/s in state-of-the-art), then system capacity is increased massively by using many wavelengths.

Transparency. Each optical channel (i.e. wavelength) can support any signal format (e.g. digital or analogue, TDM etc.)

Wavelength rerouting and switching. Can switch wavelengths and route signals by wavelength, adding an extra dimension to network design.

Advantages of WDMTransparent mediaLong haul transmissionHigh capacityUse existing optical fibersHigh performance-to-cost ratioReliabilityEasy upgrading

Brief Introduction to CWDM CWDM (Coarse Wavelength Division Multiplex) The CWDM greatly reduces the system cost while providing certain amount of wavelengths and transmission distance within 100 km. Difference between CWDM and DWDM:

WDM Components: MUXWDM multiplexer: used to combine several different wavelengths onto one fiber:

Should have low insertion loss.

MUX

1432

1 2, 3 ,4

WDM Components: DMUXWDM demultiplexer: used to remove several different wavelengths from one fiber:

Should have low insertion loss, high selectivity

DEMUX

1432

1 2, 3 ,4

WDM Components: EDFAs and FiltersOptical amplifier (EDFA): used to provide gain to wavelengths in the 1.55 m band.Tuneable optical filter: used to filter out a single wavelength for a photodetector to produce a tuneable receiver:

InputPassband tuned tothird wavelength

Output

WDM Components: Tunable lasers, add/drop MUXTuneable laser diodes (figures of merit are large wavelength tuning range, high-speed tunability, high data rate transmission, rigid wavelength stability and repeatability).Add/drop multiplexers for selective wavelength routing/extraction:

Input

addAdd

Application: Wavelength-selective WDMProvides fixed wavelength links for N transmitter/receiver pairs over a single fiber:

MUX

1432

1 2, 3 ,4

DEMUX

1432

Application: Broadband WDMMore flexible: offers broadcast and select:

Receivers can tune in to any of the broadcast wavelengthsPower splitter/combiner has 10 log N dB loss: need EDFA

N x 1

1 x N

Filter12n113PowercombinerPowersplitter

EDFA

Experimental WDM Local Area Networks

LAMBDANET and Rainbow are star topologies with N wavelengths assigned to N nodes (i.e. no wavelength re-use).

Alternative topologies are possible, e.g. chain and ring.

The following diagram shows a four-node ring network where add-drop multiplexers (ADM) are employed to allow wavelength re-use.

Ring Network

4,5,6

2,3,6

1,2,4

1,3,5

1 2 3 1 2 3 2 4 6 2 4 6 1 4 5 1 4 5 3 5 6 3 5 6

NODE 1NODE 2NODE 4NODE 3RING NETWORKADM

Wavelength assignment table

Alternative assignments are possible, as long as wavelengthsare not in contention with one another; e.g. next diagram

Wavelength assignment

1,3,5

1,2,4

2,3,6

4,5,6

2 4 6 2 4 6 1 2 3 1 2 3 3 5 6 3 5 6 1 4 5 1 4 5

NODE 1NODE 2NODE 4NODE 3

Ring Networks

Number of wavelengths added at each node equals the number that are received: all add/drop multiplexers are the same.

Advantages: full interconnection between nodes is possible, i.e. any node can talk to any other. One might expect N 2 wavelengths would be needed to achieve this, but by re-using wavelengths as shown above, need far fewer. (e.g. for N = 4, only need 6, not 16).

Choosing the right systemWhen having to move traffic on spans strecthing more than 800 km, it is obvious for many reasons to select the DWDM system over the CWDM or an SDH system for that matter.

OptiSystemOptiSystems wide range of applications includes:Optical communication system design from component to system level at the physical layerCATV or TDM/WDM network designPassive optical networks (PON) based FTTxFree space optic (FSO) systemsRadio over fiber (ROF) systemsSONET/SDH ring designTransmitter, channel, amplifier, and receiver designDispersion map designEstimation of BER and system penalties with different receiver modelsAmplified system BER and link budget calculations

OptiSystem graphical user interface (GUI)

20 Gbps, WDM transmission over 600 km

Simulation ParameterBit rateParametersSystem limitation20 Gbps (Optical Link with optical amplifier + WDM)Loss, chromatic dispersion, optical signal to noise ratio (OSNR), four wave mixing (FWM), Self-phase modulation (SPM), Polarization mode dispersion (PMD)OSNR limitedEye distortion limited

Loss and Loss Compensation

Typical Values

TransmitterTransmitter consists Pseudo-Random Bit Sequence Generator at 2.5 GbpsNRZ Pulse Generator (convert binary to electrical pulse)Continuous Wave LaserMach-Zender Modulator

8 transmitter with 100 GHz channel spacing.

Optical Receiver Receiver ConsistsPhotodetector Filter 3R (Re-amplify + Regenerator + Reshaping)

Transmission System

Dispersion Compensators

System Parameter

Transmitted and Received Pulse

TxRx

Optical Spectrum Analyzer

At MUX After travel 600 Km

WDM Analyzer

Eye Diagram

ResultMin BER is 2.85e-60We have successfully transmitted 20 Gbps bit with very low bit error

8x2.5 Gbps = 20 Gbps

Thanks